    Patent Document 1: Japanese Unexamined Patent Application Publication No. 2001-135021    Patent Document 2: International Publication Pamphlet No. 01/008145    Patent Document 3: International Publication Pamphlet No. 02/101733
For example, in read-only, that is, ROM (Read Only Memory) type optical disc media such as a CD (Compact Disc), a DVD (Digital Versatile Disc), a BD (Blu-ray disc: trademark), and a HD-DVD (High Definition DVD), music, pictures, games, application programs, and other information data are recorded in an area called a content area in a predetermined recording modulation method.
For example, many content holders use these read-only optical disc media as means for providing contents because of low production cost due to excellent mass-productivity.
Processes for manufacturing a read-only optical disc medium, for example, a DVD, roughly include a mastering process for producing an optical disc master with a laser beam; a shaping and deposition process for producing a number of disc substrates with a stamper produced from the optical disc master and forming a film on the disc substrates; and a bonding process for bonding a pair of two optical discs having a thickness of 0.6 mm together with an adhesive having a predetermined thickness so as to form a DVD disc medium having a thickness of 1.2 mm.
A concavo-convex pattern provided on the stamper is transferred onto the disc substrates mass-produced with the stamper in the shaping and deposition process. In other words, a recording data sequence of pits and lands serving as a concavo-convex pattern is formed on a portion to be an information recording surface, and this recording data sequence forms spiral or concentric recording tracks. The concavo-convex shape of the information recording surface on which pits and lands are provided is covered with a metal alloy reflective film.
After a disc is completed, laser light emitted from a reproduction apparatus is reflected by the pits and lands. In pit sequences, lands between pits are also called as “spaces”.